The present invention relates to a gel composition and use thereof. More specifically, the present invention relates to a gel composition which comprises a reversible gelling agent, an irreversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt, wherein a first gel composition in which only the reversible gelling agent functions is reversible in the conversion between a gel and a solution and by functioning the irreversible gelling agent in the first gel composition, a second gel composition can be formed irreversibly; and a process for the preparation of the same.
The present invention also relates to a gel electrolyte composition comprising the gel composition, and a process for the preparation of the same.
The present invention further relates to a solid electrolyte laminate containing the gel electrolyte composition
The term xe2x80x9csolid electrolytesxe2x80x9d means substances having high ion conductivity in a solid state. Of those substances, a high molecular weight solid electrolyte which uses a high molecular weight substance as a solid has recently attracted particular attentions as an electrolyte for lithium secondary batteries in the next generation and researches on it have been made briskly in the world.
Compared with the conventional electrolyte solution, such a high molecular weight solid electrolyte does not presumably cause liquid leakage and can be molded freely, for example, into a thin film. The conventional non-aqueous high molecular weight solid electrolyte is however accompanied with a problem such as a markedly low electrical conductivity compared with that of the electrolyte solution. For example, non-aqueous high molecular solid electrolytes obtained by complexing a polymer material such as a chain polymer (e.g., polyethylene glycol or polypropylene glycol) or a comb-type polymer such as polyphosphazene, with an electrolyte salt are conventionally known, but those having an electrical conductivity exceeding 10xe2x88x923 S/cm at room temperature have not yet been found.
In recent days, practical use of various non-aqueous gel electrolytes has been studied and a non-aqueous gel electrolyte having an electrical conductivity of 10xe2x88x923 S/cm or more, which is close to that of an electrolyte solution, has been proposed. Such a gel electrolyte is a material wherein an electrolyte salt is dissolved in a gel formed from a polymer material and a non-aqueous organic solvent, and can be obtained by dissolving the electrolyte salt, together with the polymer material or a precursor thereof, in the organic solvent and then solidifying (gelling) the resulting solution.
The conventional gel electrolytes however involve a problem that compared with an electrolyte solution, the contact with the surface of an electrode is poor, so that resistance between the gel electrolyte and the surface of the electrode is large. Such a large resistance between the gel electrolyte and the surface of the electrode prevents the effective use of the electrical conductivity which the gel electrolyte itself has, resulting in the impossibility of the practical use of it as an electrochemical element. Particularly when the electrode has not a flat surface, it is difficult to bring the conventional gel electrolyte into good contact with the surface of the electrode.
The present invention has been made to overcome the above-described problems of the conventional solid electrolyte.
Accordingly, one object of the present invention is to provide a novel gel composition useful as a solid electrolyte. Particularly, the object of the present invention is to provide a gel composition which can be treated as a solid electrolyte, can be adhered closely with the surface of an electrode and can be used as an electrochemical element in a desired form.
Another object of the present invention is to provide a process for the preparation of the gel composition.
Still another object of the present invention is to provide a gel electrolyte composition comprising the gel composition.
Further object of the present invention is to provide a process for the preparation of the gel electrolyte composition.
Still further object of the present invention is to provide a solid electrolyte laminate comprising the gel electrolyte composition.
The gel composition according to the present invention comprises a reversible gelling agent, an irreversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt.
The process for the preparation of the gel composition according to the present invention comprises a first step of heating a gel mixture comprising a reversible gelling agent, an irreversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt to a first temperature region at which the reversible gelling agent functions, to convert the gel mixture into the corresponding sol, and molding the sol into a desired shape; and a second step of heating the sol to a second temperature region at which the irreversible gelling agent functions, to irreversibly gel the sol.
The gel electrolyte composition according to the present invention comprises a reversible gelling agent, an irreversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt.
The process for the preparation of the gel electrolyte composition according to the present invention comprises a first step of heating a gel mixture comprising a reversible gelling agent, an irreversible gelling agent, an electrolyte salt and a solvent for the electrolyte salt to a first temperature region at which the reversible gelling agent functions, to convert the gel mixture into the corresponding sol, and molding the sol into a desired shape; and a second step of heating the sol to a second temperature region at which the irreversible gelling agent functions, to irreversibly gel the sol.
The solid electrolyte laminate according to the present invention comprises a solid electrolyte thin film having a layer of the reversible sol-gel composition laminated on at least one surface thereof.
The gel composition according to the present invention is in the gel form at room temperature (e.g., 25xc2x0 C.). By heating the gel composition to a first temperature region (for example, 40 to 70xc2x0 C.), it can reversibly be converted into a sol. Accordingly, the gel composition of the present invention can be molded into a desired shape under the sol state of the first gel composition, and by gelling the sol, good contact with a substrate can be maintained. By heating such a first-stage gel composition to a second temperature region higher than the upper limit of the first temperature region, the first-stage gel composition can be gelled irreversibly, so that a stable shape can be maintained while maintaining the good contact with the substrate.
Similarly, the gel electrolyte composition of the present invention can be adhered closely to the surface of an electrode even when the surface is not flat, by converting the electrolyte composition into a sol and laying it closely along the surface. The shape can be maintained stably by gelling it irreversibly. In addition, the electrolyte gel composition of the present invention has a high electrical conductivity.
Since the solid electrolyte laminate according to the present invention has a layer of the above-described gel electrolyte composition as an interface layer, it can also be adhered closely onto the surface of an electrode by utilizing the reversible sold-gel transformation. By the irreversible gelation, its shape can be maintained stably.
The reversible sol-gel type electrolyte composition or solid electrolyte laminate according to the present invention and also an electrochemical element containing it can therefore be used advantageously as, for example, a solid electrolyte in a lithium secondary battery.